וְנָגַ֧ף יְהוָ֛ה אֶת־מִצְרַ֖יִם נָגֹ֣ף וְרָפ֑וֹא וְשָׁ֙בוּ֙ עַד־יְהוָ֔ה וְנֶעְתַּ֥ר לָהֶ֖ם וּרְפָאָֽם׃
Rashi on Isaiah
And...shall plague Heb. נָגֹף. This is an expression of smiting.
Rashi on Isaiah
plaguing and healing And after the plague, He will create a cure for them.